Recovery of fatty and rosin acids



United States Patent O 3,510,468 RECOVERY OF FATTY AND ROSIN ACIDS Paul D. Patrick, Jr., and Frank J. Ball, Charleston, and

Joseph C. McManus, Jr., Mount Pleasant, SC, assignors to Westvaco Corporation, a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 621,444, Mar. 8, 1967. This application Feb. 19, 1969, Ser. No. 800,735

Int. Cl. C09f 1/02 US. Cl. 260-97.7 13 Claims ABSTRACT OF THE DISCLOSURE CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our copending application Ser. No. 621,444, filed Mar. 8, 1967 now abandoned.

BACKGROUND OF THE INVENTION This invention pertains to an improved process of separating fatty acids, rosin acids, or mixtures thereof from highly colored and odorous non-carboxylic acid constituents normally associated with such acids derived from vegetable sources. Fatty acids and rosin acids of vegetable orgin are obtained from any diverse sources, such as, the foots from caustic refining of soya, cottonseed, coconut, corn, peanut, linseed, safflower, and rapeseed oils, the black liquor from the alkaline digestion of wood,

and the solvent extracts of pine stumps. The acids or their soap salts from the above sources are associated with varying percentages of other vegetable derived, noncarboxylic acid materials and the recovery of the acids is principally a problem of separating the non-desirable, non-acid materials from the acids.

By far the greatest problem of separating acids from non-acid components occurs in the case of tall oil obtained from the black liquor from the alkaline digestion of wood. Crude. tall oil is a dark colored mixture of faty and rosin acids containing about 6 to 10 percent by weight of various other woodand lignin-derived constituents such as polycyclic hydrocarbons, sterols, organic mercaptans and phenolic materials. The relatively small quantity of these various constituents cause crude tall oil to be highly colored and of very strong odor.

The current practice is to fractionally distill crude tall oil to separate the rosin and fattey acids and to remove the greater portion of the odorand color-forming constituents. During the fractional distillation much of the odor causing materials are removed in a highly volatile heads fraction and much of the color-forming constituents are left in the extremely. high boiling pitch fraction. While fractional distillation'removes many of the undesirable constituents by their difference in volatility from that of the my and rosin acids, a certain portion of these constituents boil in the same temperature range as the acids and cannot be easily removed. Presence of the undesirable constituents causes the various fatty and rosin acid fractions to be of greatly increased color and de- 3,510,468 Patented May 5, 1970 creases the utility of these fractions in many areas, such as in varnishes, coatings, and resins, where color is of extreme importance and other areas, such as rubber polymerization where their chemical reactivity is deleterious in the desired reaction.

Though the quantity of type and impurities associated with acids or their soaps in foots and extracts of pine wood varies from that of tall oil, the problem are in general the same, although not as severe.

Other attempts at removing colorand odor-forming constituents of tall oil fatty acid and rosin acid soaps have included treating the soaps with clay, steam, phos phorous (US. Pat. 2,441,198) and bleaching with hydrosulfite and peroxide (German Pat. 694,142). Although treatment with any or a combination of these produces some improvement in color or odor, none approach the improvement of the Sulfoalkylation of the instant invention.

Another well known operation to remove the non-acid materials is by tall oil soap extraction disclosed in US. Pats. 2,558,543; 2,530,809; 2,530,810; 2,866,781; and 2,573,890. While much work has been done on solvent extraction processes, it has not been generally practical to conduct such operations since the solvent does not remove much of the color-forming constituents in the tall oil and these undesirable constituents interfer with the process of exraction.

It is the primary object of this invention to provide a process for easily removing colorand odor-forming constituents from soaps of fatty and rosin acids including unsaponifiables from fatty and rosin acids.

SUMMARY OF THE INVENTION- It has been found that substantial color and odor reduction of fatty and rosin acid fractions can be achieved by the sulfoalkylation of soaps of these acids and further improvement is noted when Sulfoalkylation is employed in conjunction with a solvent extraction step. Sulfoalkylation causes certain of the color-forming constituents, which are normally oil-soluble and distill in the same temperature range as the fatty or rosin acids, to be converted to watersoluble materials. When the soaps are acidified to free the fatty or rosin acids, a substantial amount of these watersolnbilized constituents are washed from the organic acid fraction and removed. When the acids are distilled, the absence of these materials will result in fractions of greatly improved color as compared to fractions obtained when distillation is accomplished without prior removal of these materials.

The Sulfoalkylation of this invention is carried out by treating aqueous solutions of fatty and rosin acid soaps with a combination of a water-soluble salt and an aldehyde. Sulfoalkylation is accomplished by heating an aqueous alkaline soap solution, either in a batch or contin=uons operation, at a temperature between F. and 500 F. in the presence of between 0.25% and 37.8% by weight of soap solids of a sulfite salt and between 0.015% and 3.0% by weight of soap solids of an aldehyde. After Sulfoalkylation, the soap is acidified to free the fatty or rosin acids, or further improved with a. solvent extraction step.

The exact nature of the materials removed by sulfoalkylation has not yet been clearly established. However, based upon the fact that these materials are made water-soluble, that they distill in the. same range as the fatty and rosin acids, and that the methoxy content of the crude soap is reduced by about 50%, it would appear that these compounds are complex phenolic compounds. While the exact nature of the reactions which occur are unknown, it appears that these complex phenolics react with the aldehyde to form phenol alcohols and these phenol alcohols are sulfonated by the sulfite to form water-solution substances. This sulfonation reaction ap parently occurs both at the alcoholic group added by the aldehyde reaction and directly on the aromatic ring of the phenol. The complex nature of the phenolic compounds is indicated by the fact that direct sulfonation of the. ring alone without adding the alcohol groups by reaction with the aldehyde will not result in any appreciable solubilization of these phenolics in water. The soap solution employed maybe a naturally occurring one, such as the black liquor soap skimmings obtained during normal tall oil recovery or the foots obtained from caustic refining of vegetable oils, or it may be specially prepared, as in the case of wood rosin, where the acids are not normally processed in any stage in soap form.

The sulfite salt employed in the sulfoalkylation may be any water-soluble sulfite salt, but preferably the alkali metal sulfites, such as ammonium sulfite, sodium sulfite or potassium sulfite. Sulfur dioxide may be employed, as this forms the alkali metal sulfite salt in the alkaline soap solution. As the treatment of the soap is conducted in an aqueous alkaline medium, the need for alkaline water solubility for the sulfite salt is quite obvious. It is greatly preferred that the cation of the sulfite salt be monovalent, because under the conditions of treatment polyvalent cations trans-saponify the sodium ion in the water-soluble soap to form a water-insoluble soap which would settle from solution resulting in a handling problem. While between about 0.25% and 37.8% by weight of soap solids of the sulfite salt can be effectively employed, the preferred range is from about 2.5% to 5.0% by weight of soap solids. In general, the greater the quantity of sulfite employed the better will be the color of the distillate product. However, the rate of improvement of color with increasing amounts of sulfite falls off very rapidly above 5.0% by Weight of soap solids of the sulfite. Consequently, above this level the small amount of color improvement can generally not justify the large quantity of sulfite required to obtain this improvement.

The aldehydes employed in this invention are those aliphatic and aromatic aldehydes that will condense with a phenol to yield an alcoholic group. Suitable aliphatic aldehydes, in addition to formaldehyde and compounds which yield formaldehyde under the conditions of reaction, such as paraformaldehyde, include acetaldehyde, propionaldehyde, crotonaldehyde, and furfural. Aromatic aldehydes include benzaldehyde and cinnamaldehyde. Because of its relative inexpensiveness and high reactivity, formaldehyde or paraformaldehyde is preferred. While between 0.015% to 3.0% by weight of soap solids of the aldehyde can be employed, it is preferred to use about 0.1% to 0.4% by weight of soap solids. Above 0.4% there is some decrease in the solubilization of color bodies apparently due to polymerization of the phenolic materials. The term sulfoalkylation is used throughout in reference to treatment of the soaps with a sulfite and an aldehyde and the term is intended, of course, to include the aromatic aldehydes. Furthermore, where the aldehyde used is formaldehyde or a formaldehyde yielding compound the term sulfomethylation is employed.

Rather than using separate sulfite salts and aldehydes, treatment of the soaps may be accomplished using a prereacted adduct of these compounds.

As in most reactions-the temperature and time of treatment are interrelated with one another and with the quantity of reactants employed. The higher the temperature the shorter will be the time required to obtain the desired color reduction. As a general rule the time of reaction is not extremely important. Times of reaction of at least five (5) minutes are employed. The initial reaction of the sulfite and aldehyde with the color bodies proceeds quite rapidly and a relatively sizable portion of these color bodies can be made water-soluble in a relatively short period of time. As the reaction proceeds, it becomes more and more difficult to solubilize the remaining color bodies resulting in a great decrease in the rate of color improvement with time of reaction. Reaction times exceeding 168 hours fail to produce additional improvements. As a result, the time employed is primarily an economic one of balancing the cost with color improvement obtained. Sulfoalkylation is normally carried out at atmospheric pressure; however, where higher reaction temperatures are used it is desirable to employ pressures up to psi.

In a batch process the quantity of soap being treated has a substantial effect on the time required to obtain a given color improvement. Utilizing the same temperature and ratio of sulfite and aldehyde to soap, a large batch requires significantly more time for treatment than does a small batch. For example, where treating five gallons of a soap solution for one hour will produce a given color improvement; treating a 5,000 gallon batch will require about 5 to 10 hours under the same conditions to achieve the same results.

Further, the solids contents of the aqueous soap solution has a pronounced effect on the solubilization of the non-acid materials. Sulfoalkylation under identical conditions is less effective on high solids content soap solutions than on low solids content soap solutions. This is felt to be due to the low fluidity of high solids soap solutions which apparently hinders obtaining intimate association of the water-soluble sulfite and aldehyde with the complex phenolic compounds which being oil-soluble tend to associate with the hydrophobic long chain portion of any fatty acids present. Consequently, it is the preferred practice to employ soap solutions having a soap solids content of from about 10% to 35%. Normally, tall oil soap skimmings are obtained having a soap solids content of about 50 to 65%. These high solids content soap solutions should be diluted to the preferred soap solids content with water. Likewise, foots which generally contain about 25 to 50% soaps solids should preferably be diluted prior to treatment.

Sulfoalkylation may be conducted in a single or multiple step operation. In a multiple step operation, the soap may be treated with either aldehyde or sulfite first followed by treatment with the other material. In the case where the sulfite treatment precedes the aldehyde treatment only sulfonation of the ring will occur during this initial step. Consequently, sufficient sulfite must be present, either residual from the sulfite treatment or added, during the aldehyde treatment to insure sulfonation of the alcohols formed. There appears to be no advantage, however, to a multistep operation and for reasons of simplicity, it is preferred to conduct the treatment of the soap with the aldehyde and sulfite simultaneously.

In addition to obtaining substantial reduction in the color of the distilled product, the present invention offers several other distinct advantages, particularly in the case of tall oil. Due to the water solubilization of the complex phenolic materials, when the tall oil soap is acidified there is a much cleaner separation of the aqueous brine from the oil phase resulting in a much more rapid settling of the water from the oil phase. Considerable time normally required for settling is thereby saved. Additionally, substantially higher yields of the valuable distilled fractions can be obtained. Up to 25% of the 20% of the material which normally would be left in the practically worthless pitch fraction can be distilled off to produce a valuable product without reducing the distilled product quality. This amounts to an approximate overall increase in product yield of about 5% of the total tall oil feed to the distillation column.

The sulfoalkylation treatment of this invention is preferably employed in conjunction with a tall oil soap extraction operation using non-polar solvents mentioned in the prior art.

The solvent extraction operation is capable of removing certain types of impurities, including odor causing constituents while the present treatment operates on a different type of impurity. By combining the two operations, almost all the impurities boiling in the range of the fatty and rosin acids can be removed permitting the production of extremely high quality products upon distillation.

The solvent extraction operation may be conducted prior to, after, or conceivably in conjunction with the sulfoalkylation of the present invention. By conducting the solvent extraction after the sulfoalkylation much easier separation of soap and solvent is achieved. For this reason, it is preferred that the solvent extraction operation follow the sulfoalkylation. The sulfoalkylated soaps may be contacted with the solvent in conventional solids handling countercurrent extraction equipment.

The solvent extraction, as shown in the prior art, may be conducted with a large number of solvents which are either water-miscible or water-immiscible, and which will dissolve sterols, rosin oils, and other high molecular weight natural materials. Suitable Water-immiscible solvents include aromatic and aliphatic hydrocarbons, high molecular weight monoalcoholics, esters, ethers and ketones. Preferred water-immiscible solvents are, however, the C to C aliphatic hydrocarbons or mixtures thereof, particularly suitable are hexane and naphtha. The solvent extraction process, as noted, may also be carried out with the addition of water-miscible solvents, such as a low molecular weight aliphatic alcohol, to the soap solution which greatly facilitates extraction of the undesirable constituents. Particularly suitable low molecular weight alcohols are those having from one to four carbons, especially iso-propyl alcohol.

In a preferred extraction operation sulfomethylated soaps are diluted with iso-propyl alcohol and undesirable constituents are extracted by contacting the alcohol diluted soaps with hexane in a countercurrent extractor having one or more stages at a temperature between 40 F. and 180 F. After recovery of the solvents, and acidification of the fatty and rosin acid soaps the purified soap skimmings produce a crude tall oil of 12% unsaponifiables and 180-187 acid number. This crude tall oil when fractionated in distillation equipment, produces a line of high quality products.

The following examples illustrates the process of this invention in the recovery of a mixture of rosin and fatty acids from black liquor soap.

EXAMPLE 1 sulfomethylation was accomplished by diluting 1,000 grams of tall oil soap skimmings containing 620 grams of soap solids with 3,000 parts by Weight of water to produce an aqueous soap solution having 15.5% soap solids content. To this soap solution was added 1.5 grams of formaldehyde and 25 grams of sodium sulfite. The resultant mixture was heated to 170 F. and held at that temperature for 5 hours. The thus treated soap solution was acidified with sulfuric acid to free the rosin and fatty acids from their soaps. After settling, the crude tall oil, decanted from the brine and washed with water, showed significant increase in yield. The crude tall oil was then vacuum distilled to obtain heads, pitch and distillate fractions. The heads fraction constituted the first 5% of the crude tall oil which distilled over, the distillate fraction constituted the next 75% portion distilled over and the pitch was the 20% residue obtained after the distillate fraction had been taken off.

EXAMPLE 2 For comparison to the sulfomethylated product of Example 1, a portion of the same tall oil soap skimmings used as the starting material of Example 1 was acidified, washed, and distilled in the same manner as above. This material, however, was not treated with sulfite or aldehyde.

Comparison of the sulfomethylated and untreated tall oil was as follows:

Dist Heads Pitch Tall oil Gardner Acid Gardner Gardner Acid sample color No. color color No.

sulfomethylated 6+ 102 7 12+ 87 Untreated 8+ 191 10- 14 It will be noted that the sulfomethylated tall oil resulted in an improvement in the color of the distillate of two Gardner color numbers. This is fairly typical of the results which can be obtained. Additionally, unlike untreated tall oil distillate products which lose about 3 Gardner colors during aging for 4-12 weeks, the colors of the distillates from the present invention are more stable. Storage for 412 weeks results in a loss of only 2 Gardner colors.

EXAMPLE 3 This example shows a solvent extraction operation used in conjunction with the sulfomethylation treatment. A 1,000 gram sample of the tall oil soap skimming used in Example 1 containing 620 grams of soap solids was diluted with 3,000 grams of water. To the resultant soap solution 3 grams of formaldehyde and 50 grams of sodium sulfite were added and the solution heated to F. for 2% hours and the temperature of the solution raised to 210 F. Where it was held for 4 hours. The treated product was diluted with an equal 'volume of isopropyl alcohol and extracted with 2,000 ml. of hexane in a six stage countercurrent batch operation. The soap after extraction was acidified to free the acids which were washed and distilled as in Example 1.

The distillate obtained had a Gardner color of 5.5. This is a 3 color improvement over the distillate obtained from the soap without any treatment (8+) and approximately one color improvement over the sulfomethylated soap without extraction (6+). Using this process the color sta bility is exceedingly good with a color loss of only /2 to 1 Gardner units resulting from 4-12 weeks storage. The acid without sulfomethylation and hexane extraction reduced the color of the distillate by approximately only one Gardner color unit to 7.5.

EXAMPLE 4 Example 3 was repeated except that during distillation a 5% heads out and a 84% distillate cut were taken leavmg a pitch residue of only 11%. While the pitch fraction was reduced by 45% thereby increasing the valuable distillate yield by 12%, the distillate had a Gardner color of only 6.

EXAMPLE 5 In a 10 gallon kettle, tall oil skimmings were treated with 2.5% Na SO and 0.3% paraformaldehyde and heated for two hours at 275 F. at a pressure of 50 p.s.1. The resulting sulfomethylated tall oil soap from this test when compared with untreated soap was:

Distillate Heads Pitch Tall oil Gardner Acid Gardner Acid Acid sample color N 0. color No. No.

sulfomethylated. 6+ 190 8 Untreated 8 187 1 0 177 Note the approximated 2 Gardner number improvement exhibited by the sulfomethylation treatment.

EXAMPLE 6 parison of the sulfomethylated tall oil soap versus the untreated tall oil soap was as follows:

It will be noted that the sulfomethylation resulted in a reduction in color in the distillate of more than 2 Gardner colors and that the treatment reduced the quantity of pitch produced by 3.5% on the crude.

It might be noted that while sulfomethylation results in a marked improvement in color, it does not appreciably change the unsaponifiable content of crude oil. On the other hand, the extraction results in less color change but reduces the unsaponifiable content of the tall oil by from 50% to 75%. When the tall oil soap skimmings were processed according to Example 1, the crude tall oil had an unsaponifiable content of 8.0%. After distillation, the heads fraction contained 30% low-boiling unsaponifiables, and the 75% distillate fraction contained 2.5 unsaponifiables. However, crude tall oil obtained in Example 4 contained only 2.5% unsaponifiables. After distillation the 5% heads fraction contained only 1.7% unsaponifiables, while the 84% distillate cut contained only 0.9% unsaponifiables. It will thus be noted that the combined treatment essentially eliminated all the distillable unsaponifiables from the tall oil, and the acids produced a high quality heads fraction which in essence increases yield by an additional 5%.

While the invention has been described and illustrated herein by references to various specific materials procedures, and examples, it is understood that the invention is not restricted to the particular materials, combinations of materials, and procedures selected for that purpose. Numerous variations of such details can be employed, as will be appreciated by those skilled in the art.

We claim:

1. The process of treating a vegetable derived soap of acids selected from the group consisting of fatty acids, rosin acids and mixtures thereof comprising; treating an aqueous solution of said soap with from 0.25% to 37.8% by weight based on soap solids of a water-soluble sulfite salt and from 0.015% to 3.0% by weight based on soap solid-s of an aldehyde selected from the group consisting essentially of ali hatic and aromatic aldehydes at a temperature of from 150 F. to 550 F. for at least 5 minutes until odor-forming and color-forming constituents are rendered water-soluble when the soap is converted to the acid form.

2. The process of claim 1 wherein said aldehyde is from the group consisting essentially of formaldehyde and formaldehyde-forming aldehydes.

3. The process of claim 1 wherein said sulfite is a water-soluble, alkali metal sulfite salt.

4. The process of claim 1 wherein said soap is extracted with a water-immiscible solvent selected from the group consisting essentially of aliphatic hydrocarbons having from five to ten carbon atoms to remove non-acid compounds from said soap.

5. The process of claim 4 wherein a low molecular weight alcohol containing from one to four carbon atoms is present with the soap during said extraction.

6. In the prOcess of recovering tall oil from black liquor soap by acidifying the black liquor soap to convert the soap to free fatty and rosin acids the improvement comprising, treating an aqueous solution of said tall oil soaps with from 0.25% to 37.8% by weight based on soap solids of a sulfite salt selected from the group con- I sisting essentially of sodium sulfite, potassium sulfite and ammonium sulfite and from 0.015% to 3.0% by weight based on soap solids of an aldehyde selected from the group consisting essentially of formaldehyde, formaldehyde-forming aldehydes, acetaldehyde, propionaldehyde, furfural, benzaldehyde and cinnamaldehyde at a temperature form F. to 550 F. for at least 5 minutes until the nonacid constituents converted to water-soluble compounds.

7. The process of claim 6 wherein between 2.5% and 5.0% by weight of said water-soluble sulfite salt and 0.1 to 0.4% by weight of said aldehyde are employed.

8. The process of claim 6 wherein the black liquor soap is at a tall oil soap solids content between 10% and 35% prior to said treatment with said sulfite salt and said aldehyde.

9. The process of claim 6 wherein said sulfite salt is sodium sulfite and said aldehyde is from the group consisting essentially of formaldehyde and formaldehyde-forming aldehydes.

10. The process of claim 13 wherein said water miscible solvent is iso-propyl alcohol.

11. The process of claim 6 wherein said treated black liquor soap is extracted with a water-immiscible solvent selected from the group consisting essentially of aliphatic hydrocarbons having from five to ten carbon atoms to remove non-acid compounds from said black liquor soap.

12. The process of claim 11 wherein said water-immiscible solvent is hexane.

13. The process of claim 11 wherein a low molecular Weight alcohol having from one to four carbon atoms is present with the soap during said extraction.

References Cited UNITED STATES PATENTS 2,530,810 11/1950 Christendom et al. 26097.7

DONALD E. CZAJ A, Primary Examiner W. E. PARKER, Assistant Examiner US. Cl. XR. 2604125, 424 

